The present invention relates to a communication device, and more particularly to a transceiver adapted to be used in an extremely noisy surroundings such as a motor race course and a construction site.
A transceiver, which is a widely-used portable transmitter, is usually used under circumstances where there is little noise. With such a transceiver, transmission between two people can be satisfactorily made without any difficulty in an environment where ambient noise is lower than 90 dB. However, if the ambient noise exceeds 90 db, the noises are picked up by the microphone, and due to the masking effect, it becomes impossible for the recipient to clearly discern the transmitted speech.
In order to solve the problem, the inventor of the present invention has proposed in Japanese Patent Laid Open 5-22784, a solid-borne sound transmitting device.
Referring to FIG. 3, the transmitting device comprises a headset 1 having an arm 2, and a vibration pickup 3 disposed on an inner end portion of the arm 2.
The headset 1 is worn over a head 4 of an operator, so that the vibration pickup 3 is pressed on a cheek 5. When the operator speaks, solid-borne vibrations generated in the cheek 5 is efficiently converted into an electrical signal by the vibration pickup 3 and transmitted to a receiving device of the recipient.
The reason the pickup 3 is abutted on the cheek 5 and not on other parts of the head is that the cheek generates vibrations, the level of which is higher than those from other parts, and that the frequency of the vibration falls within a spectrum space wherein words of the speaker is sufficiently articulated. In addition, cheeks are less sensitive to pain and other discomforts even after a long-term use.
The inventor of the present invention has also proposed in Japanese Patent Application No. 3-131436 an earphone shown in FIGS. 4 and 5, which blocks ambient noises.
Referring to FIG. 4, the earphone has a dynamic exciter 9 housed in a plastic casing 11 having an upper opening. A cylindrical yoke 14 is resiliently mounted with appropriate stiffness in the casing 11 by a plurality of dampers 13. A magnet 15 is axially provided in a central portion of the yoke 14, and a central pole 16 is mounted on the magnet 15. A metalic diaphragm 12 is mounted on the top of the casing 11 to hermetically close the casing 11. A voice coil 17 is attached on the underside of the diaphragm 12 so that, when the diaphragm 12 is mounted, the voice coil 17 is disposed in an annular space between the yoke 14 and the central pole 16 without touching them.
Referring to FIG. 5, when using the earphone, an earplug 8 is inserted in an external auditory canal 7 of an ear. The earplug 8 is made of a sound insulating material such as a closed-cell polymer foam, for example, urethane foam.
In order to hear the transmission, the dynamic exciter 9 is held to contact the earplug 8. When the voice coil 17 of the exciter 9 is applied with an audio signal ViN through a lead 18, an alternating field is generated by the voice coil 17, and a magnetic field is caused by the magnetic circuit comprising the magnet 15 and the center pole 16. Hence the voice coil 17 is moved in the magnetic field as a result of electromagnetic induction in accordance with the frequency of the input audio signal V.sub.IN. The voice coil 17 accordingly elastically vibrates the metal diaphragm 12, thereby forming elastic waves. Namely, the exciter 9 is different from a regular sound radiating speaker in that it is a shaker which causes elastic vibration of the diaphragm 12. The ear plug 8, an end of which is in contact with the diaphragm 12, serves as a couplant for propagating the elastic sound waves, which vibrate the tympanic membrane through the external auditory canal 7. Hence, an intelligible sound can be heard without interruption by ambient noises.
However, the above described transmitting device and the receiving device are two different devices. It will be more convenient if the devices are assembled into one.